Ink jet printer start-up and shutdown

Abstract

An ink jet printer includes a print head for producing at least one jet drop stream from a fluid filament emerging therefrom, and charge electrode for inducing electrical charges on drops formed from the fluid filament. The charge electrode is movable into and out of an operating position in which it is adjacent and at least partially surrounds the fluid filament. A deflection field is established prior to start-up in which the field has a non-zero electrical potential in the region of the fluid filament. At start-up and shutdown of the printer, the charge electrode is retracted from its normal operating position and drops are charged by the deflection field. As a consequence, the charge electrodes are not contaminated by ink from the unstable jets. The drops in the jet drop streams are, however, charged and deflected to a catcher by the deflection field. After stable operation is obtained, the charge electrode is moved into its normal operating position. At shutdown of the printer, this sequence of steps is reversed.

What is claimed is: 
     
       1. An ink jet printer, comprising: print head means for producing at least one jet drop stream from a fluid filament emerging therefrom,   charge electrode means for inducing electrical charges on drops formed from said fluid filament when said charge electrode means is in a first position at least partially surrounding said filament, said charge electrode means being movable into a second position remote from said fluid filament,   catcher means, positioned to one side of the path of said jet drop stream, for catching drops deflected thereto,   deflection field means for producing an electrical deflection field in the region between said print head means and said catcher means, said field extending in a direction such that drops carrying a charge of a first polarity are deflected toward said catcher means, and said field having a non-zero potential of a second polarity in the region of said fluid filament, and   means for moving said charge electrode means from said second position to said first position after start-up of said printer and initiation of said jet drop stream, and for moving said charge electrode means from said first position to said second position prior to shutdown of said printer, whereby drops in said jet drop stream are charged by said deflection field and deflected to said catcher means at start-up and shutdown of said printer.   
     
     
       2. The ink jet printer of claim 1 in which said deflection field means comprises: first and second deflection electrodes positioned symmetrically with respect to said jet drop stream and   means for applying an electrical potential of a first polarity to said first deflection electrode and for applying a second electrical potential of a second polarity to said second electrode, the absolute value of said electrical potential of a first polarity being less than the absolute value of said electrical potential of a second polarity, such that said field has a non-zero potential of a second polarity in the region of said fluid filament and drops are charged by said field when said charge electrode means is positioned in said second position remote from said fluid filament.   
     
     
       3. The ink jet printer of claim 2 in which said second deflection electrode is positioned on the same side of said jet drop stream as said catcher means. 
     
     
       4. The ink jet printer of claim 2 in which said second deflection electrode is formed of a porous material and defines a vacuum cavity to which a partial vacuum is applied, whereby drops striking said second deflection electrode are ingested into said vacuum cavity. 
     
     
       5. The ink jet printer of claim 1, in which said deflection field means comprises: first and second deflection electrodes positioned on opposite sides of said jet drop stream, said second electrode being substantially closer to said jet drop stream than said first deflection electrode, and   means for applying first and second electrical potentials of first and second polarities to said first and second deflection electrodes, respectively, said first and second electrical potentials being of substantially equal magnitude, such that said field has a non-zero potential of a second polarity in the region of said fluid filament and drops are charged by said field when said charge electrode means is in said second position, remote from said fluid filament.   
     
     
       6. The ink jet printer of claim 1 in which said print head means produces a plurality of jet drop streams arranged in at least one row, and in which said charge electrode means includes a charge plate defining a plurality of open-sided charge electrodes along one edge of said charge plate. 
     
     
       7. In an ink jet printer including a print head for producing at least one jet drop stream, charge electrode means for inducing electrical charges on the drops formed in said jet drop stream, a catcher positioned to one side of the jet drop stream for catching drops deflected thereto, and deflection field means for producing an electrical deflection field in the region between said print head and said catcher, said field extending in a direction such that drops carrying a charge of a first polarity are deflected toward said catcher means, the method of printer start-up, comprising the steps of: retracting said charge electrode means from its normal operating position,   producing an electrical deflection field having a non-zero potential of a second polarity in the region adjacent said print head,   initiating jet drop stream formation, whereby the drops formed are electrically charged to a first polarity by said electrical deflection field and subsequently deflected to said catcher, and   moving said charge electrode means into its normal operating position so as to shield said jet drop stream in the region of drop formation, while continuing to charge said drops to a first polarity with said charge electrode means so as to catch said drops.   
     
     
       8. The method of claim 7 in which the step of producing an electrical deflection field includes the steps of: providing first and second deflection electrodes positioned symmetrically to either side of said jet drop stream, and   applying an electrical potential of a first polarity to said first electrode and an electrical potential of a second polarity to said second electrode, said electrical potential of a second polarity having an absolute magnitude greater than the absolute magnitude of said electrical potential of a first polarity, whereby the potential of said field in the region where drops are formed is non-zero and of a second polarity to thereby induce a charge of a first polarity on the drops.   
     
     
       9. The method of claim 7 in which the step of producing an electrical deflection field includes the steps of: providing first and second deflection electrodes positioned to either side of said jet drop stream, said second deflection electrode being closer to said jet drop stream than said first electrode, and   applying an electrical potential of a first polarity to said first deflection electrode and an electrical potential of a second polarity to said second deflection electrode, said potentials applied to said deflection electrodes being of substantially equal magnitude.   
     
     
       10. The method of claim 7 in which the step of moving said charge electrode means into its normal operating position includes the step of providing an electrical field potential of a second polarity in the region of drop formation with said charge electrode means so that drops continue to be charged to said first polarity and drops continue to be deflected to said catcher. 
     
     
       11. In an ink jet printer including a print head for producing at least one jet drop stream, charge electrode means for inducing electrical charges on the drops formed in said jet drop stream, a catcher positioned to one side of the jet drop stream for catching drops deflected thereto, and deflection field means for producing an electrical deflection field in the region between said print head and said catcher, said field extending in a direction such that drops carrying a charge of a first polarity are deflected toward said catcher means, the method of printer shutdown, comprising: producing an electrical deflection field having a non-zero potential in the region adjacent said print head, while shielding the jet drop stream with said charge electrode means in the region of drop formation from said deflection field,   charging drops formed in said jet drop stream to a charge level of said first polarity by said charge electrode means,   retracting said charge electrode means from its normal operating position to expose the drops then being formed to said electrical deflection field, whereby said drops are charged to a charge of a first polarity by said electrical deflection field and therefore are deflected to said catcher, and   terminating jet drop stream formation.   
     
     
       12. The method of claim 11 in which the step of producing an electrical deflection field includes the steps of: providing first and second deflection electrodes positioned symmetrically to either side of said jet drop stream, and   applying an electrical potential of a first polarity to said first electrode and an electrical potential of a second polarity to said second electrode, said electrical potential of a second polarity having an absolute magnitude greater than the absolute magnitude of said electrical potential of a first polarity, whereby the potential of said field in the region where drops are formed is non-zero and of a second polarity, thereby to induce a charge of a first polarity on the drops.   
     
     
       13. The method of claim 11 in which the step of producing an electrical deflection field includes the steps of: providing first and second deflection electrodes positioned to either side of said jet drop stream, said second deflection electrode being closer to said jet drop stream than said first deflection electrode, and   applying an electrical potential of a first polarity to said first deflection electrode and an electrical potential of a second polarity to said second deflection electrode, said potentials applied to said deflection electrodes being of substantially equal magnitude.   
     
     
       14. The method of claim 11 in which the step of charging drops by said charge electrode means includes the step of providing an electrical field potential of a second polarity in the region of drop formation.